Different types of roller presses are used in the cement and minerals industries to crush, grind and comminute material. One type of roller press is a High Pressure Grinding Roller (HPGR) system. HPGR technology has traditionally been used in the cement industry for many years and over the past few years HPGR has also proven itself on more complex and harder ores in the mineral industry.
Most generally, in HPGR the feed material is exposed to very high pressures for a short time when it passes through rollers. The high pressure of the rollers causes the formation of micro-cracks and boundary weakening in the feed particles and thus generates a substantial amount of fine material (e.g.—in the form of briquettes or fine dusts). The pressed fine material product from the HPGR can be fed directly to a ball mill which works to further comminute such material. As a significant amount of work has been effected before the ball mill, HPGR makes it possible to increase the throughput of the ball mill and in most cases significantly reduce the specific power consumption of the total milling system.
Roller presses typically include two grinding rollers—for example, a stationary roller and a second moveable roller. The stationary and moveable rollers are spaced apart from each other to define a nip (or gap) between the rollers. The rollers are rotated to comminute material that may pass through the nip. The second moveable roller may be moveable away from the first roller to widen the nip and may be moveable closer to the stationary roller to narrow the nip. Examples of roller presses may be appreciated from U.S. Pat. Nos. 880,035, 4,484,879, 4,838,156, 4,905,910, 5,192,030, 5,211,108 5,354,002, 5,405,091, 5,454,520, 5,505,389, 5,601,242, 5,918,823 and U.S. Patent Application Publication Nos. 2009/0314868 and 2009/0236455.
The grinding rollers are typically driven and controlled by force generation devices. Force generation devices may be any device capable of applying force to the moveable bearing housings (i.e.—the housings which contain the grinding rollers) or directly to the grinding rollers in order to widen or narrow the nip. The force generation devices may further be capable of absorbing forces from the moveable grinding rollers and may be configured to help maintain a resultant width of the nip between the rollers when comminuting crushable material.
For example, force generation devices may be devices such as hydraulic cylinders or rams, springs and the like. By way of further example, FLSmidth's HPGR is typically equipped with a bilateral hydraulic pressing system, which ensures that the pressing force is largely uniform during the comminution process. The system serves to protect the press against localized overloading and stress. The system contains a skew control feature for limiting the grinding gap differential. Components for pressurizing the cylinders are integrally mounted and pre-piped on a common base consisting of a pump (with standby pump), filter, safety and control valves, pressure transmitter, and reservoir. Typically, four double-acting hydraulic cylinders, mounted in pairs are utilized.
However, such force generation devices are typically very heavy and difficult to remove from the HPGR system for maintenance/replacement because such devices sit directly under the top frame of the roller press. As a result of such placement, there is significant downtime on the HPGR system when such force generation devices are required to be maintained or replaced. In addition, such placement results in a removal or repair process which is more dangerous than one that has less restricted access, and auxiliary tools that occupy a significant amount of space. By way of example, in the design of the frame for FLSmidth's HPGR, as illustrated in FIG. 6, before the heavy force generation devices can be hoisted out of the system, the pins of the top member of the frame assembly must be disconnected and thereafter portions of the HPGR must be moved or rotatably dropped to the ground in order to expose the force generation devices. By way of further example, the roller press system disclosed in U.S. Pat. No. 7,451,945 similarly requires pins to be removed from the top member of the frame assembly and for the entire, heavy overhead frame to be rotated into the open position before the force generation devices can be hoisted for replacement or repair. When in the open position, the rotated portion of the frame occupies a significant amount of space next to the HPGR system, can cause safety concerns and takes a great deal of time and wasted energy to rotate into position. Similar examples of such systems are found in DE20207014764, US 2013/025476 and US 2014/048634.
A new roller press is needed that permits the force generation device(s) to be more easily removed for replacement or repair without removing or rotating the top member of the frame assembly. Such a roller press and method for performing maintenance with such a press would result in less operational downtime, higher resultant throughput, safer maintenance conditions and a smaller footprint during such a process, without limitation.